Process for preparing polytetrahydrofuran

ABSTRACT

Polytetrahydrofuran, tetrahydrofuran copolymers, diesters or monoesters of these polymers are prepared by polymerizing tetrahydrofuran in the presence of at least one telogen and/or comonomer on a heterogeneous carrier catalyst which contains on an oxidic carrier material as active mass a catalytically active amount of at least one oxygenous molybdenum and/or tungsten compound and, when the precursor compounds of the active mass have been applied to the carrier material precursor, has been calcined at temperatures of between 500° C. and 1000° C. The catalyst used contains a promotor which comprises at least one element or a compound of an element of the 2nd, 3rd including the lanthanides, 5th, 6th, 7th, 8th or 14th group of the periodic system of elements.

SUMMARY

Polytetrahydrofuran, tetrahydrofuran copolymers, and diesters ormonoesters of these polymers are prepared by the polymerization oftetrahydrofuran in the presence of at least one telogen and/or comonomerover a heterogeneous supported catalyst which contains an activecomponent comprising a catalytically active amount of at least oneoxygen-containing tungsten and/or molybdenum compound on an oxidicsupport material and which, following application of the precursorcompounds of the active component to the support material precursor, hasbeen calcined at temperatures of from 500° C. to 1000° C., where acatalyst is used which contains a promotor comprising at least oneelement of Group 2, 3 (including the lanthanides), 5, 6, 7, 8 or 14 ofthe Periodic Table or a compound of such element.

DESCRIPTION

The present invention relates to an improved process for the preparationof polytetrahydrofuran, tetrahydrofuran copolymers, and diesters ormonoesters of these polymers by the polymerization of tetrahydrofuran inthe presence of at least one telogen and/or comonomer over aheterogeneous supported catalyst, which contains as active composition acatalytically active amount of at least one oxygen-containing molybdenumand/or tungsten compound on an oxidic support material and which hasbeen calcined, following application of the precursor compounds of theactive composition to the support material precursor, at temperatures offrom 500° C. to 1000° C.

Polytetrahydrofuran (“PTHF”), also known as poly(oxybutylene glycol), isa broadly used intermediate in the plastics and synthetic fiberindustries and serves inter alia for the preparation of polyurethane,polyester and polyamide elastomers. In addition, it is, as are also someof its derivatives, a valuable auxiliary for many applications, such asdispersing agents, or for the process of decolorizing (“de-inking”)waste paper.

PTHF is advantageously prepared on an industrial scale by polymerizationof tetrahydrofuran over catalysts in the presence of reagents, theaddition of which makes it possible to control the chain length of thepolymer chains and thus to set the average molecular weight to thedesired value (chain-terminating agents or “telogens”). Control takesplace in this case by varying the type and amount of the telogen. Byselecting suitable telogens functional groups can be additionallyintroduced at one or both ends of the polymer chain. Thus for example byusing carboxylic acids or carboxylic acid anhydrides as telogens themonoesters or diesters of PTHF can be prepared. Other telogens areeffective not only as chain-terminating agents, but are alsoincorporated in the growing polymer chain of the PTHF, that is to saythey not only operate as a telogen, but also as a comonomer and cantherefore be equally well designated as a telogen or as a comonomer.Examples of such comonomers are telogens containing two hydroxyl groupssuch as the di-alcohols. Examples of such di-alcohols are ethyleneglycol, propylene glycol, butylene glycol, 1,4-butanediol,2-butyne-1,4-diol,1,6-hexanediol or low molecular weight PTHF. The useof such comonomers leads to the preparation of tetrahydrofurancopolymers. In this manner it is possible to chemically modify the PTHF.One example thereof is the use of the telogen 2-butyne-1,4-diol, theaddition of which causes a proportion of C≡C triple bonds to be presentin the polymer chains of the PTHF. Such modified PTHF can, due to thereactivity of these triple bonds at these sites, be further refinedchemically, for example by hydrogenation of the triple bonds to doublebonds, by subsequent addition polymerization of different monomers(“grafting”) for varying the properties of the polymer, cross linkagefor the formation of polymers having a comparatively rigid structure, orother measures commonly used in polymer chemistry. Total hydrogenationof the triple bonds that are present is likewise possible and generallyleads to PTHF having a particularly low color index.

DE-A 4,433,606 describes a process for the preparation of PTHF, PTHFdiesters of C₂-C₂₀ monocarboxylic acids or PTHF monoesters of C₁-C₁₀monocarboxylic acids by the polymerization of tetrahydrofuran over aheterogeneous catalyst in the presence of one of the telogens water,1,4-butanediol, PTHF having a molecular weight of from 200 to 700dalton, a C₁-C₁₀ monocarboxylic acid or a carboxylic anhydride derivedfrom C₂-C₂₀ monocarboxylic acids or mixtures of these telogens, wherethe catalyst is a supported catalyst which contains a catalyticallyactive amount of an oxygen-containing tungsten or molybdenum compound ormixtures of these compounds on an oxidic support material and which,following application of the precursor compounds of theoxygen-containing molybdenum and/or tungsten compounds to the supportmaterial precursor, has been calcined at temperatures of from 500° C. to1000° C.

WO 96/09335 teaches a process for the preparation of PTHf or PTHFmonoesters of C₁-C₁₀ monocarboxylic acids by the polymerization oftetrahydrofuran over a heterogeneous catalyst in the presence of one ofthe telogens water, 1,4-butanediol, PTHF having a molecular weight offrom 200 to 700 dalton, a C₁-C₁₀ monocarboxylic acid or mixtures ofthese telogens, where the catalyst is a supported catalyst whichcontains a catalytically active amount of an oxygen-containing tungstenor molybdenum compound or mixtures of these compounds on an oxidicsupport material and which, following application of the precursorcompounds of the oxygen-containing molybdenum and/or tungsten compoundsto the support material precursor, has been calcined at temperatures offrom 500° C. to 1000° C.

The prior German patent application DE-A 19641481.4 of Sep. 10, 1996teaches a process for the preparation of polytetrahydrofuran, copolymersof tetrahydrofuran and 2-butyne-1,4-diol, diesters of these polymerswith C₂-C₂₀ monocarboxylic acids or monoesters of these polymers withC₁-C₁₀ monocarboxylic acids by the polymerization of tetrahydrofuran inthe presence of one of the telogens water, 1,4-butanediol,2-butyne-1,4-diol, polytetrahydrofuran having a molecular weight of from200 to 700 dalton, a C₁-C₁₀ monocarboxylic acid or a carboxylic acidanhydride derived from C₂-C₂₀ monocarboxylic acids or mixtures of thesetelogens over a heterogeneous supported catalyst which contains acatalytically active amount of an oxygen-containing tungsten ormolybdenum compound or mixtures of these compounds on an oxidic supportmaterial and which, following application of the precursor compounds ofthe oxygen-containing molybdenum and/or tungsten compounds to thesupport material precursor, has been calcined at temperatures of from500° C. to 1000° C. and which has been activated before use aspolymerization catalyst by treatment with a reducing agent.

Since the economical value of a PTHF process catalyzed using aheterogenous catalyst greatly depends on the productivity of thecatalyst, it is an object of the present invention to increase thecatalyst activity of the known catalysts used in THF polymerization inorder to achieve higher polymer yields and/or space-time yields.

Accordingly we have found a process for the preparation ofpolytetrahydrofuran, tetrahydrofuran copolymers, and diesters ormonoesters of these polymers by the polymerization of tetrahydrofuran inthe presence of at least one telogen and/or comonomer over aheterogeneous supported catalyst which contains an active componentcomprising a catalytically active amount of at least oneoxygen-containing tungsten and/or molybdenum compound on an oxidicsupport material and which, following application of the precursorcompounds of the active component to the support material precursor, hasbeen calcined at temperatures of from 500° C. to 1000° C. and which ischaracterized in that a catalyst is used which contains a promotorcomprising at least one element of Group 2, 3 (including thelanthanides), 5, 6, 7, 8 or 14 of the Periodic Table or a compound ofsuch element.

The polymerization catalysts used in the process of the invention aresupported catalysts on an oxidic support material, which containoxygen-containing molybdenum or tungsten compounds or mixtures thereofacting as the catalytically active component (“active composition”) andat least one promotor of Group 2, 3 (including the lanthanides), 5, 6,7, 8 or 14 of the Periodic Table or compound of such promotor.

Suitable support materials are generally oxidic supports, for examplezirconium dioxide, titanium dioxide, hafnium oxide, yttrium oxide,iron(III) oxide, aluminum oxide, tin(IV) oxide, silicon dioxide, zincoxide or mixtures of these oxides, but we prefer to use zirconiumdioxide or titanium dioxide, titanium dioxide being particularlypreferred.

Suitable active compositions are oxygen-containing molybdenum ortungsten compounds or mixtures of such compounds, where the use ofoxygen-containing tungsten compounds or mixtures of oxygen-containingtungsten compounds with molybdenum compounds containing oxygen, in whichthe content of tungsten compound predominates, is preferred. Weparticularly prefer to use catalysts in which the active compositioncomprises, apart from the usual impurities, virtually onlyoxygen-containing tungsten compounds.

The exact chemical and physical structure of the active composition isunknown. For the sake of simplicity the content of active composition inthe catalyst is based on the trioxides of tungsten or molybdenum.

The catalysts generally contain from 0.1 to 50 wt %, preferably from 5to 40 wt % and more preferably from 5 to 25 wt %, of active composition,calculated as MoO₃ or WO₃, based on the total weight of the catalyst.

Suitable components of the promotor are metals or compounds of metals ofGroups 2 (Be, Mg, Ca, Sr, Ba), 3 (Sc, Y, La) including the lanthanides(Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, Lu), 5 (V, Nb, Ta),6 (Cr), 7 (Mn, Re), 8 (Fe, Ru, Os) and 14 (Ge, Sn, Pb) of the PeriodicTable.

Preferred is the use of Ba, Y, La, Ce, Nb, Cr, Mn, Fe, Ru and Sn orcompounds thereof and the use of Nb, Fe, Y and Cr or compounds thereofis especially preferred.

The promotor can comprise the said elements individually or in admixturewith each other or in admixture with compounds thereof or be a mixtureof the compounds thereof. The exact chemical and physical structure ofthe components of the promotor is unknown. Without binding ourselves toa model, it is assumed that not later than the point following thecalcining treatment of the catalyst the components of the promotor arenot present in the form of the elements, but for the sake of simplicitythe content of promotor in the catalyst is stated as being the contentof metal in the promotor.

The catalysts generally contain from 0.01 to 30 wt %, preferably from0.05 to 20 wt % and more preferably from 0.1 to 15 wt % of promotor,calculated as the sum of its components in the form of their elementsand based on the total weight of the catalyst. In many cases, especiallyas regards the preferred or particularly preferred uses of promotorconstituents, the promotor concentration ranges from 0.2 to 3 wt %. Theamount of promotor required to optimize a certain desired property ofthe PTHF to be synthesized (activity, average molecular weight ordispersion) or the type and amount of its components can be simplydetermined by carrying out a few routine tests.

In addition to the active composition and the promotor, the catalyst canalso contain sulfur and/or phosphorus, a catalyst containing addedsulfur being preferred. Without binding ourselves to a model, it isassumed below that the sulfur in the catalysts of the invention ispresent as sulfate and the phosphorus as phosphate. The catalysts cancontain from 0.01 to 15 wt %, preferably from 0.1 to 10 wt %,particularly 0.25 to 5 wt %, of oxygen-containing sulfur or phosphoruscompounds, calculated as sulfate or phosphate and based on the totalweight of the catalyst.

The preparation of the catalysts to be used in the process of theinvention is carried out in a similar manner to the methods described inDE-A 4,433,606 or WO-A 96/09335, incorporated rated herein by reference,for the preparation of the catalysts used in the processes described insaid specifications for the preparation of PTHF. The catalysts to beused in the process of the invention differ from those revealed in DE-A4,433,606 and WO-A 96/09335 substantially only in the presence of thepromotor.

The preparation of the catalysts generally starts with a supportmaterial or a precursor of a support material which is converted to thesupport material during the preparation of the catalyst, especiallyduring calcination, as far as possible or completely. We preferablystart from support precursors containing a number of hydroxyl groups,such as freshly precipitated hydroxide. It is however likewise possibleto use commercial oxides as supports or hydroxides which have been driedfollowing precipitation thereof. The precipitation of hydroxides takesplace in known manner, for example by addition of ammonia or aqueousammonia solution to soluble or hydrolysable compounds of those elementsof which the oxides form the support material, and separation of theprecipitate. Subsequent drying can take place at from 20° to 350° C.,preferably at from 50° to 150° C., and particularly from 100° to 130°C., at atmospheric pressure or reduced pressure.

A very suitable support is titanium dioxide predominantly present in theanatase form. We prefer to use a titanium dioxide containing not morethan 35 wt % of the rutile and brookit modifications.

This titanium dioxide can be prepared, for example, by calcinationduring the preparation of the catalyst from titanium hydroxide. Titaniumhydroxide can be produced by precipitation from a hydrolysable titaniumstarting compound. Suitable hydrolysable starting compounds for thepreparation of the titanium hydroxide are for example the halides,nitrates or alkoxides. Examples of suitable starting compounds aretitanium tetraisopropylate, titanyl chloride, titanyl nitrate, titaniumtetrachloride or titanyl sulfate. The hydroxide is preferablyprecipitated from solutions of these compounds by the addition ofammonia solution. Suitable solvents for the titanium starting compoundsare all solvents in which the starting compounds are soluble and can beprecipitated by means of aqueous ammonia solution. Examples of suchsolvents are the C₁-C₈ alcohols, such as methanol, ethanol, propanol,isopropanol, n-butanol, isobutanol, tert-butanol, pentanol, hexanol or2-ethylhexanol. It is basically also possible to precipitate titaniumhydroxide from these alcoholic solutions by the addition of water ordilute sulfuric acid.

When the hydroxide is precipitated, there is generally formed a gel-likeprecipitate, which gives a radio-amorphous powder on drying. It ispossible that these radio-amorphous precipitates are composed of notonly the hydroxides but also of a large number of different compoundscontaining hydroxyl groups, for example different oxide hydrates, metaacids, or polymeric, water-insoluble hydroxide complexes. Since theexact chemical composition of these precipitates cannot be determinedhowever, it is assumed, for the sake of simplicity, that they comprisethe hydroxide. Thus the term “hydroxide” is used for the purposes ofthis application as a collective term denoting the precipitatescontaining hydroxyl groups as produced by the above methods. From thehydroxide water may be extracted, by a commonly used drying method, forexample by heating to 90° to 150° C. and/or by the use of reducedpressure such that a free-flowing powder having good handling propertiesis formed.

The precursor compounds of the active composition and the components ofthe promotor are applied to the supports or support precursors by knownmethods.

One method, preferred for its simplicity, is the impregnation of thesupport or support precursor with a solution of precursor compounds.Basically it is possible to use arbitrary solvents, pure or in admixturewith each other, and arbitrary precursor compounds, where the precursorcompounds should be soluble in the solvents or solvent mixture usedunder the process conditions used, such as temperature andconcentration. The choice of solvents and precursor compounds can be metas routine matter by reference to a solubilities table. We prefer to usewater as solvent. To increase the solubility, particularly that of themolybdenum or tungsten compounds, an aqueous ammonia solution may beused as solvent.

The water-soluble precursor compounds of the active composition can be,for example, the water-soluble salts of molybdic acid (H₂MoO₄) ortungstic acid (H₂WO₄), such as are produced for example when molybdenumtrioxide ortungsten trioxide is dissolved in aqueous ammonia or theisopoly compounds resulting therefrom are acidified.

The water-soluble precursor compounds of the promotor constituents canbe the water-soluble salts of the corresponding metals. Provided thatthe corresponding anion does not impair the properties of the catalystfor polymerization of THF, which may be readily ascertained by carryingout simple routine tests, suitable salts can be selected from asolubilities table. Examples of suitable salts are barium acetate,yttrium nitrate, lanthanum or cerium sulfate or nitrate, niobium oxalateor niobium/ammonium oxalate, ammonium dichromate, manganese nitrate,iron sulfate or nitrate, ruthenium chloride or tin sulfate.

If it is desired to prepare a catalyst having a content of sulfur and/orphosphorus, there is added to the impregnation solution at least onesulfur and/or phosphorus compound. The choice of this compound or thesecompounds is not subject to any particular limitation. Examples ofuseful sulfur- or phosphorus-containing compounds are sulfuric acid,soluble sulfates such as ammonium sulfate or ammonium hydrogen sulfateor the corresponding sulfites or hydrosulfites, phosphoric acid, solublephosphates such as ammonium phosphate or the ammonium hydrogenphosphates or the corresponding phosphites. The addition of sulfurand/or phosphorus can take place in a simple manner by the use ofsoluble promotor precursor constituets containing sulfur or phosphorus,for example their sulfates, unless this is offset by unduly lowsolubility in the impregnating materials.

It is possible to apply the promotor constituents or the precursorsthereof prior to, together with, or after the active composition ortheir precursors or optionally prior to, together with, or after theaddition of sulfur and/or phosphorus. It is likewise possible to applyvarious components of the active composition, the promotor, sulfur orphosphorus in a number of impregnation steps. It is also possible toapply the total amount of active composition, promotor and optionallysulfur and/orphosphorus not in a single step but successively in anumber of impregnation steps.

If several impregnation steps are used, drying and/or calcination cantake place between the separate steps, and advantageously at least onedrying step is carried out.

It is generally simpler, however, and therefore a preferred method, toapply, simultaneously, the entire active composition and all promotorconstituents and any sulfur and/or phosphorus to be added, byimpregnating the support or support precursor with a solution whichcontains both at least one precursor compound of the active compositionand at least one precursor compound of the promotor and, optionally, thesulfur and/or phosphorus to be added followed by drying and calcination.

The impregnated supports or support precursors are generally dried attemperatures of from 80° to 500° C., preferably from 100° to 350° C., atatmospheric pressure or reduced pressure. This produces the catalystprecursor.

In a possibly advantageous embodiment, the preparation of the catalystprecursor may be carried out by intimately blending the said precursorcompounds of the active composition and the promotor and any sulfurand/or phosphorus to be added, as undissolved compounds, with thesupport or support precursor in suitable apparatus, for example akneader or pug mill, in which case auxiliaries such as polyethylene orbutylene glycols can be added. This method can also involve the use ofcompounds which are insoluble in water or other solvents, for exampleMoO₃, WO₃, H₂WO₄, Ba₅O₄ or FeOOH. It is also conceivable to combineimpregnating steps with previous blending of solid constituents. Forexample, a mixture of titanium dioxide and a tungsten compound such asH₂WO₂can be first and this then dried if necessary before it isimpregnated with a solution of a promotor precursor, e.g. manganesenitrate. Alternatively, a support or support precursor can be first ofall impregnated with a soluble compound such as ammonium dichromate andthen, optionally after drying, blended with a solid tungsten compoundsuch as WO₃. It is possible, in all of these steps, to add sulfurand/phosphorus if so desired.

The supports or support precursors thus treated are, like the catalystprecursors produced exclusively by impregnation, dried before furthertreatment.

Another way of preparing the catalyst precursors comprisesco-precipitation of a hydroxide-containing support precursor with aprecursor of the active composition and a precursor of the promotor andalso, optionally, with added sulfur and/or phosphorus followed bydrying, as in the case of impregnation. This co-precipitation can takeplace, for example, in the same manner as the precipitation of ahydroxide by the addition of ammonia or aqueous ammonia solution to asolution containing soluble or hydrolysable precursor compounds ofsupport, active composition and promotor and, optionally, containingadded sulfur and/or phosphorus. This synthesis method can beadvantageous when it is necessary to prepare a particularly homogeneouscatalyst. In a manner similar to the aforementioned method relating tothe processing of undissolved precursor compounds, the co-precipitationcan be carried out, if desired, by first of all precipitating only thesupport precursor together with the precursor of the active compositionand/or the promotor precursor and/or the added sulfur and/or phosphorus,and then to separate and dry this solid material before applying theremaining components by one or more impregnation steps or, if desired,by further precipitation.

Another possibility is the preparation of a catalyst using a pyrogenictechnique, that is to say by pyrolysis or burning of a mixture ofprecursor compounds of the support, active composition and promotor,which method generally provides particularly pure catalysts. Suitableprecursor compounds are those which are sufficiently volatile and can bepyrolyzed or burned to oxides free from residue, for example the elementalkoxides or element chlorides. For example, a catalyst for use in theprocess of the invention can be prepared by pyrolysis of a mixture ofTi(O^(i)Pr)₄, W(OEt)₅ and Nb(OEt)₅ followed by calcination. In this casealso, it is possible to dope with sulfur and/or phosphorus by adding atleast one volatile pyrolyzable sulfur and/or phosphorus compound, e.g.H₂S, SO₂, SO₃ or PH₃ or volatile esters of sulfuric or phosphoric acidsuch as the methyl or ethyl esters.

Irrespective of the synthesis method used, all of the catalystprecursors are subjected to calcination in air at temperatures of from500° to 900° C., preferably from 550° to 850° C. and more preferably attemperatures of from 600° to 800° C. to be converted to the finalcatalysts. Calcination at these high temperatures is important for theachievement of a high conversion rate and thus a high space-time yieldduring the polymerization of THF. At lower calcining temperatures thecatalysts still effect THF polymerization but only at uneconomically lowconversion rates.

According to the invention, the catalysts can be additionally activatedby treatment with a reducing agent following calcination. Activation ofthe catalysts by preliminary hydrogenation can take place in a mannersimilar to the method described in detail in the prior German patentapplication DE-A 19641481.4 of Sep. 10, 1996. Generally, for thispurpose the catalyst is treated with a reducing agent followingcalcination and before it is used in the polymerization of THF.

Suitable reducing agents are basically all reducing agents which leaveno residues on the catalysts treated therewith or the residues that areleft are such as are inert to the polymerization of tetrahydrofuran andhave no detrimental effect on the use of the polymerization products.

The reducing agents used can be for example organic compounds which havea reducing action on the catalysts in their calcined form, such asalcohols, aldehydes, carboxylic acids or hydrocarbons, while it is alsopossible to use bifunctional or polyfunctional compounds such as hydroxyacids, hydroxy aldehydes, polyalcohols, dialdehydes or polyaldehydes ordiacids or polyacids or salts of organic reducing agents, of which theammonium salts are preferred.

Examples of useful organic reducing agents are straight-chain orbranched-chain aldehydes containing from one to ten carbon atoms such asformaldehyde or acetaldehyde, propionaldehyde, butyraldehyde,isobutyraldehyde or glyoxal, straight-chain, branched-chain or cyclicmonocarboxylic or dicarboxylic acids or their salts such as formic acid,ammonium formate, acetic acid, propionic acid, butyric acid, isobutyricacid, oxalic acid, lactic acid, benzoic acid, citric acid or ascorbicacid, straight-chain, branched-chain or cyclic alcohols or hydrocarbonssuch as methanol, ethanol, propanol, isopropanal or aldoses such asglucose.

Examples of inorganic reducing agents that can be used in the process ofthe invention are hydrogen compounds such as hydrides with for examplealkali metal tetrahydridoboranates such as sodium tetrahydridoboranate,9-borane-bicyclononane, catechin borane, a solution of di-borane intetrahydrofuran or in various ethers, alkali metaltetrahydridoaluminates such as lithium tetrahydridoaluminate, or simplebinary hydrides such as the hydrides of alkali metals or alkaline earthmetals, for example lithium hydride, sodium hydride or calcium hydride.

Preferred reducing agents used are gases containing hydrogen such aspure hydrogen or hydrogen in admixture with other gases. Particularlypreferred is the use of hydrogen either in pure form or diluted with aninert gas such as nitrogen or argon. For example mixtures of nitrogenand hydrogen are highly suitable. Such mixtures can contain up toapproximately 60 vol % of hydrogen in nitrogen, while hydrogen contentsof up to 40 vol % or 20 vol % are likewise suitable. Generally however,a hydrogen content of up to 10 vol % is adequate. The content ofhydrogen can also be successively raised during the course of thereducing reaction in order to avoid an excessively strong exothermalreaction at the start of the reaction. For example the ratio by volumeof inert gas to hydrogen at the commencement of the reaction can beapproximately 99:1 (or even higher, e.g. 99.5:0.5) which is generallylowered as reduction proceeds, as otherwise the necessary reductiontimes are prolonged. Ratios of 98:2,95:5, 90:10, 80:20, 60:40 or 50:50or even lower values down to pure hydrogen can be set successively ordirectly, use being made, if desired, of finely stepped transitionsbetween the mixtures having different hydrogen concentrations merging ona continuous rise in the hydrogen content. The rate of increase of thehydrogen content and the final value of this hydrogen content areadvantageously set according to the heat produced during the reductionso as to avoid an excessive generation of heat. An excessive generationof heat has been produced, for example, when the liberated heat ofreaction can no longer be removed by the cooling system of the reductionreactor. An excessive generation of heat has also been produced, forexample, when the catalyst reaches, on account of the liberated heat ofreaction, a temperature which impairs its properties for thepolymerization, for example when the catalyst melts, sinters orundergoes other thermal changes, at least partially, caused for exampleby thermal decomposition or evaporation of organic components such asextrusion auxiliaries or pelleting auxiliaries.

The treatment of the calcined catalyst with the reducing agent generallytakes place at temperatures of from 20° C. to 500° C. When reduction isnot effected using hydrogen-containing gases the preferred temperaturerange is from 100° C. to 400° C. But if the reduction is carried outusing solid, liquid or dissolved reducing agents the preferred reductiontemperatures range from 20° to 200° C.

When reduction is not effected by treatment of the catalyst with gaseousmaterials the pressure sure used is generally immaterial. If in thiscase the reducing agent is converted partially or completely to gaseousoxidation products as reduction of the catalyst proceeds, the reactionpressure used should not hinder the formation of these gaseous oxidationproducts however, that is to say a pressure which is not unduly high isgenerally advantageous. It can be for example between 1 and 5 barabsolute. Preferably, the reduction is carried out under standardpressure. If thereduction is carried out with gaseous reducing agents,it can take place at standard pressure or elevated pressure, for examplebetween 1 bar and 300 bar (absolute) and preferably ferably between 1bar and 50 bar (absolute).

The reduction time is generally from 10 minutes to 100 hours, preferablyfrom 30 (minutes to 50 hours and more preferably from 1 hour to 24hours.

The reducing agent is generally used in an amount of from 0.01 to 100mol, particularly from 0.1 to 50 mol per gram of calcined catalyst andpreferably in an amount of from 0.1 to 10 mol per gram of calcinedcatalyst.

The conditions of reduction temperature, reduction time and amount ofreducing agent which are optimal for a given composition of the calcinedcatalyst over the general ranges stated above must in each case bedetermined empirically by routine reduction experiments and reactiontests, since they are governed by the content of active component in thecatalyst, the type of active component used, the type of support usedand the type and amount of doping agent used. Generally, reduction iscomplete when the heat usually generated at the commencement ofreduction has substantially subsided, after which a subsequent reductionperiod of from 5 minutes to 5 hours, advantageously from 10 minutes to 2hours, can follow.

Preferably, reduction is carried out by treatment of the catalyst with agaseous reducing agent and more preferably by treatment of the catalystwith a mixture of hydrogen and nitrogen. For this purpose the catalystis advantageously placed in a fixed bed reactor in the form of powder orshaped particles and the gas mixture containing hydrogen is passedthrough the catalyst bed. The reactor has a temperature control systemwhich makes it possible, on the one hand, to dissipate the heatgenerated during the reaction and, on the other hand, to maintain therequired reaction temperature. Following hydrogenation, the catalyst,can be formed into shaped particles, if this has not already been doneprior to hydrogenation.

The catalysts which can be used in the present invention may be employedin the process of the invention for the polymerization of THF in theform of powder, for example when the process is carried out insuspension, or advantageously as shaped particles, e.g. in the form ofcylinders, balls, rings, spirals or chips, especially when the catalystis present in a fixed bed, as is preferred when use is made of, say,loop reactors or the process is carried out continuously.

The process of the invention can be carried out in a manner similar tothe processes described in detail in DE-A 4,433,606 or WO 96/09335,which are included herein by reference. The use of the comonomer2-butyne-1,4-diol in the process of the invention can follow the linesof the method described in detail in the German patent application No.19507399.1 (PCT application PCT/EP 96/00702), which is included hereinby reference.

EXAMPLES

Preparation of the Catalyst

The catalysts were synthesized by the following technique: a kneadablecomposition was prepared by the addition of titanium hydroxide and thepromotor compound or the precursors thereof to a solution of tungsticacid (H₂WO₄, prepared by the use of the corresponding amount of tungstentrioxide WO₃) to a 32 wt % strength aqueous ammonia solution. The amountof ammonia solution used was such as to ensure that the tungstic acidcould just be dissolved without leaving a residue. If the compositionwas not kneadable in this form, small portions of about 10 mL of more ofammonia solution were added until a kneadable composition formed. Thiscomposition was kneaded for 120 minutes in a laboratory kneader(exceptions being the catalysts of Example 1: 150 min; Example 3: 90 minand Example V2: 180 min), then dried over a period of 12 hours at 120°C. and finally sifted after drying. The sifted powder was pelleted toform 3×3 mm pellets. The pellets were calcined in air for 2 hours at650° C.±25° C.

The finished catalyst pellets were analyzed by means of quantitativefluorescent spectroscopy to determine their content of tungsten(calculated as tungsten trioxide, WO₃) and promotor (calculated asmetal).

The weights of the starting materials used and also the analysis resultsare listed in Table 1, together with the results of the polymerizationexperiments.

THF Batch Polymerization

The batch polymerization experiments were carried out in 100 mL glassflasks equipped with reflux condensers under a blanket of nitrogen. 20 gof catalyst pellets, which had been dried for 18 hours at 180° C./0.3mbar prior to use in order to remove adsorbed water, were heated in 40 gof THF containing butanediol (butanediol concentration 2000 ppm) over aperiod of 24 hours at 50° C. Then THF containing water (1% H2O) wasadded to the reaction mixture and the catalyst separated by filtration.The catalyst was washed three times with 40 g of THF each time and thefiltrates were combined and concentrated at 70° C./20 mbar in a rotationevaporator and then for a further 30 min at 150° C./0.3 mbar in a bulbtube. The PTHF forming as bottoms was weighed and analyzed by gelpermeation chromatography (GPC). Table 1 lists the test results obtainedon the catalysts 1 to 10 and the results of two comparative examples V1and V2.

The dispersity D as a measure of the distribution of molecular weightsof the polymers produced according to the examples was calculated fromthe ratio of the weight average of the molecular weight (M_(w)) and thenumber average of the molecular weight (M_(n)) according to the equation

D=M _(w) /M _(n)

M_(w) and M_(n) were determined by GPC, a standardized polystyrene beingused for calibration. From the chromatograms the number average M_(n)was calculated according to the equation

M _(n) =ΣC _(i)/(C _(i) /M _(i))

and the weight average M_(w) according to the equation

M _(w)=(Σ(C _(i) *M _(i))/ΣC _(i)

in which C_(i) stands for the concentration of the individual polymerspecies i in the polymer mixture and in which M_(i) denotes themolecular weight of the individual polymer species i.

As shown by the experiments, the use of promoted catalysts in theprocess of the invention leads to an increase in yield in all cases.

The smallest measured increase in yield is found in Example 2. Even herehowever, this increase in yield is as much as 5% better than the yieldobtained in the corresponding comparative example V2 (catalyst having acomparable content of active composition). The examples thus show thatthe use of the process of the invention distinctly increases thecapacity of existing plants for the preparation of PTHF without the needfor plant conversion or, conversely, future plants can have smallerdimensions and will therefore involve lower investment costs.

TABLE 1 Starting materials, analysis results and experimental findingsPromotor or precursor Analysis [wt %] PTHF Synthesis Ti hydroxide H₂WO₄Amount Promotor Yield Ex. [g] [g] Type [g] WO₃ (metal) [%] M_(n) D 1 20053 BaSO₄ 2 18.4 0.73 24 8310 2.4 2 150 32 SnSO₄ 29 17.2 9.20 21 8740 3.73 150 40 Y(NO₃)₃ × 6 H₂O 2 22.7 0.25 28 6800 3.2 4 148 40 Ce(SO₄)₂ 223.3 0.68 25 6850 2.8 5 150 30 “Nb.-ox.”*) 10 17.7 0.54 34 7000 5.0 6140 40 (NH₄)₂Cr₂O₇ 10 23.2 2.60 27 8230 3.4 7 148 40 Mn(NO₃)₂ 2 23.50.33 23 7160 2.9 8 140 40 FeSO₄ 10 24 1.30 31 6660 4.0 9 160 29 FeSO₄ 917.7 1.20 30 8620 3.4 10  150 29 RuCl₃ 5.5 17.8 1.20 25 8640 3.8 V1 15040 — 23.6 — 22 7870 2.2 (comp.) V2 1000  200  — 18.4 — 20 5790 2.5(comp.) *)“ammonium-niobium oxalate”: niobium oxalate containingammonium oxalate (obtainable from H.C. Stark)

What is claimed is:
 1. A process for the preparation ofpolytetrahydrofuran, tetrahydrofuran copolymers, and diesters ormonoesters of these polymers by the polymerization of tetrahydrofuran inthe presence of at least one telogen and/or comonomer over aheterogeneous supported catalyst which contains an active componentcomprising a catalytically active amount of at least oneoxygen-containing tungsten and/or molybdenum compound and a promotercomprising at least one element of Group 2, 3 (including thelanthanides), 5, 6, 7 8 or 14 of the Periodic Table, or a compound ofsuch elements on an oxidic support material and which, followingapplication of the precursor compounds of the active component andpromoter to the support material precursor, has been calcined attemperatures of from 500° C. to 1000° C.
 2. A process as defined inclaim 1, wherein the catalyst used is supported on titanium dioxide. 3.A process as defined in claim 1, wherein the catalyst used has an activecomposition consisting of at least one oxygen-containing tungstencompound.
 4. A process as defined in claim 1, wherein the catalyst usedcontains from 0.1 to 50 wt % of active composition, calculated as MoO₃or WO₃, based on the total weight of the catalyst.
 5. A process asdefined in claim 1, wherein the catalyst used contains a promotercomprising at least one element, or at least one compound of suchelement, selected from the group consisting of Ba, Sn, Y, La, Ce, Nb,Cr, Ma, Fe and Ru.
 6. A process as defined in claim 5, wherein thecatalyst used contains a promoter comprising at least one element, or atleast one compound of such element, selected from the group consistingof Nb, Fe, Y and Cr.
 7. A process as defined in claim 1, wherein thecatalyst used contains a promoter in an amount of from 0.1 to 15 wt %,calculated as the elementor elements and based on the total weight ofthe catalyst.
 8. A process as defined in claim 1, wherein the catalystused has been additionally doped with sulfur and/or phosphor.
 9. Aprocess as defined in claim 1, wherein the catalyst used has beenactivated after calcination but prior to use in the polymerization bytreatment with a reducing agent.
 10. A process as defined in claim 1,wherein the telogen and/or comonomer used is water, 1,4-butanediol,2-butyne-1,4-diol, polytetrahydrofuran having a molecular weight of from200 to 700 dalton, a C₁-C₁₀ carboxylic acid or a carboxylic anhydridederived from a C₂-C₂₀ monocarboxylic acid or a mixture of said telogensand/or comonomers.
 11. A process as defined in claim 10, wherein2-butyne-1,4-diol is used as comonomer.
 12. A process as defined inclaim 10, wherein acetic anhydride is used as telogen.